Vacuum tube periodic relay



Feb. 11, 1936. G. vE. Hmmm, JR 2,030,794'

-vncuul TUBE: rsnIoDIc RELAY Filed oct. 26. 1934 lrammed ret. 11. 193s UNITED STATES PATENT oFFlcE t This invention relates to thermionic control systems and more particularly to a device for cyclically opening and closing relay contacts at very low speeds.

Within limits, any desired period of opening and closing the relay can be obtained by a proper choice of the circuitparameters. 'I'hus the system may be used` in many adaptations, as for example the periodic switching on and of! of electric signs. controlling the intermittent iiashing of a beacon light or intermittently controlling the radiation from a radio beacon set. i

The principal object ot this invention is to provide a system for periodically opening and closing a set of relay contacts at any predetermined slow speed by means purely electrlcal with# out the advent of any moving mechanical parts. Another object oi' this invention is to provide a system for periodically opening and closing a set oi' contacts that is both economical to construct and economical to operate. Other objects and advantages of this invention will appear from the detailed description and the drawing in which the single iigur'e shows schematically a preferred em.-

bodiment of the invention.

In the drawing reference character I represents a thermionic tube having a cathode or iilament 2, a control grid 3 and an anode or plate l. The cathode 2 is shown connected so as to be energized by a battery or other appropriate source of potential 5. 'I'he control grid 3 is connected by means of the lead to one end of a coil 1 con`k stituting one of the windings of a transformer 6 1. The-other end oi' the coil 1 is connected by means of lead I! to one oi' the terminals' oi' a condenser 9. theother terminal oi' which is connected through lead I1 to the cathode 2 of the tube. A resistance III is connectedin shunt with the condenser 9. A condenser 8 is connected by means oi leads I1 and I8 between the lcontrol grid 3 and the cathode 2. 'I'he plate or anode 4 of the thermionic tube I is connected by means of lead I4 to one end of the coil 6 of thetransformer 6 1. 'Ihe other end oi the coil 6 is connected by means of lead I5 to one end of the primary winding oi' the iron cored audio frequency transformer I2. The 'other end o! the primary winding oi.' the transformer I2 is connected by means of the lead I6 to the positive terminal of a battery or other appropriate source of anode potential II. 'I'he negative terminal of the source of potential II is connected by way of lead I1 to the cathode 2. The secondary winding of the transformer I2 is appropriately connected to the input electrodes o1' the amplifying thermionic tube 2l iluence of the source of anodepotential II`.

while the relay 22 is-connected tov'be' energized by current iiow in said tube. Armaturel 22 conto either contact 24 or 25 depending upon the energization ofthe relay 22.

'trolled by the relay 22 isadapted to be connected d The above description has dealt only with the actual circuit connections, the parameters of the circuit components will now be dealt with. With avac'uum tube of the'type quite generally known as a II2 employed in the oscillator circuit (tube 1( I) with a potential of approximately 90 volts lmpressed at'II and with winding 6 of the transformer 6 1 consisting of approximately 54 turns of No. 26 single covered silk wire wound into a coil 21A inchesiin diameter and 2% -inches long closely coupled to coil 1 consistingoi' approximately 63 turns ot No. 22 single covered silk wire wound into a coil 3 inches in diameter and 2% inches long and with a condenser o! .0005 microiarad connected at 8 and a condenser ot 2 microfarads connected at 9- shunted by a resistance ot 2 megohms at III the circuit will have a time constant of approximately seven seconds, that is, seven seconds will elapse between successive energizations or deenergizations o! the relay 22. With a resistance of l megohm at I0 and with the other circuit parameters as above the time constant of the system will be approximately one second. Variation oi the time constant oi' the system can lalso be obtained by varying the capacities of the condensers 8 and/or il or by varying them or either of them simultaneously with a variation of the resistance III.

By varying the condensers I and 9 and omitting the resistance I0 very low speeds result, a time constant oi' over two minutes has been attained. This form of control is only efiicient over a period of several hours. As the grid oi thel osc.y tube becomes more and more highly charged the time constant gradually becomes greater.

Using the resistance I0 together with proper condensers at 8 and 9 the -timing is highly eilicient. A relay circuit built exactly as shown in the drawing should run indeiiniiy at the set time constant. A relay in operation continuously for over iifty hoursshowed absolutely no measurable change in time constant.

The exact theory of operation o! the system is not denitely known although it is believed that the system functions as follows: With the energization of the cathode 2 a great swarm -ot electrons is drawn over to the anode l under the in- This gives rise to a current surge in the coil 6 of transformer 6 1 and causes a potential to build up across the coil 1. This potential quickly charges the condenser 8. which is of relatively small capacity, by way of leads I8 and I9 and the condenser 9 which is of relatively great capacity. Since coil 1 and condenser 8 constitute a tuned resonant circuit it is apparent that the potential of the control electrode 3 connected to one end of said coil is excited cyclically at a frequency determined by the L C constants of the circuit as aresult of the initial surge of current in the coil 1. This cyclic variation of the potential oi the control electrode of the tube causes the anode current to have a component which varies at that frequency. This varying anode current causes the oscillations to persist due to the transformer action at 6 1. However, as the oscillation persists the average value of the anode current decreases due to the accumulation of electrons on the control grid forcing its average potential more negative until ultimately the control grid becomes so highly charged that oscillations cease. Before oscillations can begin again the charge on the control grid l must leak ofi by way oi the reslstancelll..

As this takes place the anode currentgradually increases until the generation of oscillations starts again at which time the foregoing cycle is repeated. i

'Ihe slow variation o! the average current in the anode circuit causes a slow variation of the potential that is induced in the secondary of the transformer I2 through the relay 22 is slow to change and hence the relay 22 only energizes or deenergizes at such times as the average anode current of the tube I is increasing or decreasing depending upon the connection of transformer I2. f For the purpose of simplicity the drawing shows the source of cathode and anode potentials as being batteries andthe thermionic tubes shown are simple triodes; however it is to be clearly understoodthat alternating current may be used to energize the cathodes of the tubes and that any desired source oidirect current may be used to supply the anode potential. Other tubes than the ones disclosed may be used as for exampleheater type tubes and/or tubes with screening grids and the like, also impedance coupling of appropriate type may be'used in lieu of the transformer I2. When the source of potential II and the primary ot the transformer I 2 are lacking in sufficient distributed capacity to make the system function properly a by-pass condenser should beconnected asshow at 26 between leads II and I1.

The novel features and the operation of this vdevice will be apparent from the foregoing description. While the device has been shown-and the structure described in detail, it is obvious that this is'not to be considered limited to the exact form disclosedandthatchangesmaybemade therein within the scope of what is claimed without departing from the spirit of the invention Having thus set forth and disclosed the nature of this invention, what is claimed is:

'1. A system for producing a relatively low frequency variation ofv the average current in the VUprimary winding of a transformer comprising a thermionic tube having a cathode, an anode and a control electrode. a source of potential connected-so as to energize said cathode, a source of anode potentiaLfan inductance coll, means connecting said source of-anode potentiaLthe primary winding of said transformer and the inductance coll in series between the cathode and the anode of said tube, a second inductance coil closely coupled to said first mentioned inductance coil,

Thus the value of the anode current -i a condenser of relatively small capacity. a cotidenser of relatively large capacity shunted by a resistance of relatively large size, means connecting the condenser of relatively small capacity between the control electrode and the cathode of said tube. means connecting one of the ends oi said second inductance coil to the control electrode, and means connecting the other end of said second inductance coil to the cathode oi' fsaid tube. said last means including the condenser o! relatively large capacity shunted by said resistance of relatively large size, whereby the potentials induced in the secondary of said transformer are of relatively low frequency.

2. A system for producing a relatively low irequency variation of the average current in the primary winding o! a transformer comprising a thermionic tube having a cathode, an anode and a control electrode, a source ot potential connect- .edsoastoenergizesaidcathodaasourceof anode potential, an inductance coil, means 'connecting said source of anode potential the primary windingof saidtransi'ormerandtheinductance coil in sones beween the cathode and the anode oi said tube, a second inductance coil1 closely coupled to said first mentioned inductance coil, a condenser oi' relatively small capacity'. a condenser o! relatively large capacity shunted by a resistance of relatively large size, means'connecting the condenser of relatively small capacity between the control electrode and the cathode ofsaidtube.meansconnectingoneoftheends ,o of said second inductance coil to the control electrode, and means connecting the other end o! said second inductance coil to the cathode of said tube, said last means including the condenser o! relatively large capacity shunted ,by said resistance ot relatively large size, and means tor selectively adjusting the sizes of the said condensers and the resistance value of said resistance o ktrodeandthccathodethereof,aniinpedanceincluded in the anode circuit, and means for utilising the slow variation in the average value of the current in said impedance for controlling the energizatlon and deenergimtion of said relay.

4. An electron tube system for cyclically energizing a relay at a very slow rate comprising a three element tube having an oscillatory circuit included between the cathode and one of the other elements thereof, a second circuit closely coupled to said oscillatory circuit included be. tween the cathode and the remaining element thereof, a condenser of relatively large capacity shunted by a variable resistance of relatively large size connected between the control electrode and the cathode thereof, an audio frequency transformer, means connecting the'primary winding of said transformer in the anode circuit of said tube, an audio frequency ampliiler having its input circuit connected to the secondary ot said transformer and a relay included in the output circuit of said amplier.

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